Regarding the question about calorie burn while cycling decreasing while using GW, posted by ha1ha1, what are you using to measure this?
If you are using anything aside from a power meter, then the figure will be seriously skewed and will be under reporting the number of calories burnt while your are using GW.
The number of calories burnt while cycling in a given time period is a result of the number of watts produced over that time period. Same thing with a light bulb: a 100w light bulb that is in use for one hour uses more electricity than a 60w light bulb in use for one hour.
So if you want an accurate measure if the number of calories burnt, you have to measure power output. Power output while cycling can only be measured using a properly calibrated power meter like an SRM, powertap or the like. Outside of competitive cyclists, not many people own power meters as they are REALLY fucking expensive. An SRM, which is regarded as the gold standard in cycling power measurement will cost you about US$2500 for a base model.
Heart rate monitors, cycling computers and other devices that are used most commonly, calculate calories used by using a set of mathematical assumptions based on your heart rate and the user data that you enter into the device. These assumptions work for the average cyclist, but such approximations go out the window when you are doping or even when you are just really fit.
I did an experiment some time back when I was racing a lot: I wore a polar heart rate monitor and also ran my SRM for the same ride. The heart rate monitor grossly under reported the number of calories reported over the course of the 4 hour ride. I was pretty fit at the time I did this experiment. i had a resting heart rate of 30-35 bpm, I raced in elite and I was in the top 20 rankings for my country at that time. "Outliers" like super fit athletes or people using products like GW do not fit into the mathematical model behind the calorie calculations used by your average heart rate monitor or cycle computer. The reason for this is that when you are using or really fit, you are much more efficient. You are doing more work with less effort.
To continue with the light bulb analogy, by taking GW, you changed your cycling body from being an average joe 100w incandescent light bulb, to a more efficient 30w compact fluorescent bulb, BUT YOU PRODUCE THE SAME AMOUNT OF LIGHT!
Basically when you are using GW, you are producing XXX watts with less effort than when you when you were not using GW. Lower effort is manifest by a lower heart rate, and this tricks your heart rate monitor or cycle computer into thinking your not working as hard and therefore not burning as many calories compared with when you were not on GW.
Your heart rate monitor or cycling computer is incorrect. If you are doing the same work, you are burning the same number of calories, by definition. Chances are, because you are on GW, you are working harder, producing more power and burning more calories, but you just don't feel it and your heart rate is lower than it would be without GW.
Hope this make sense. Sorry for the long post.